patman: Don't return the series in FixPatches()

There is no need for this function to return the same object that was
passed in. Drop the return value.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>

tools/patman/patchstream.py

@@ -477,7 +477,6 @@ def FixPatches(series, fnames):
             print
         count += 1
     print('Cleaned %d patches' % count)
-    return series
 
 def InsertCoverLetter(fname, series, count):
     """Inserts a cover letter with the required info into patch 0